An exhaust system of an internal combustion engine is usually equipped with means for cleaning or treating the exhaust gases removed from the internal combustion engine. It may be necessary in this connection to introduce a liquid educt into the exhaust gas stream, to evaporate it therein and to mix it with the exhaust gas. It may be necessary, for example, to mix a fuel with the exhaust gas upstream of an oxidation catalytic converter in order to bring about heating of the exhaust gas stream by an exothermal reaction of the fuel in the oxidation catalytic converter. The heated exhaust gas stream can then be used downstream of the oxidation catalytic converter to heat another exhaust gas treatment means, for example, another catalytic converter or a particle filter, to operating temperature or regeneration temperature. Furthermore, SCR systems are known which operate with selective catalytic reaction and are equipped with an SCR catalytic converter, which takes up NOx from the exhaust gas stream. A suitable reducing agent, for example, ammonia or urea, preferably an aqueous urea solution, is added to the exhaust gas stream upstream of the SCR catalytic converter. The ammonia will then bring about a conversion of the nitrogen oxides present into nitrogen and water in the SCR catalytic converter.
It applies to all educts fed in the liquid form into the exhaust gas stream that the desired effect can be achieved satisfactorily only if sufficient evaporation of the educt as well as sufficient mixing of the gaseous educt with the exhaust gas stream can take place between the site at which the liquid educt is introduced and a site at which the educt is consumed. The mixing and/or evaporating means mentioned in the introduction, which are arranged in the flow path of the exhaust gas between the site at which the educt is introduced and the site at which the educt is consumed, are used for this purpose.